This mod is called “Elemental Arrows” and is made by a guy called Risugami. This is an actual content mod and not just a skin, so the installation is a little trickier, but the payoff is totally worth it.

Elemental Arrows gives you 4 new kinds of arrows; explosive arrows, fire arrows, ice arrows, and of course, egg arrows… The egg arrows is just a gag weapon, so it’s not some sort of weird super weapon. They are made in the way that you’d expect, just replace the standard flint with gunpowder for explosive, coal for fire, bucket of water for ice, and egg for egg.

“Crafting an explosive arrow only gives you one arrow, and it explodes upon impact. Crafting a fire arrow gives you one arrow, that will ignite stuff upon impact. Crafting an ice arrow gives you four arrows, that will freeze water into ice, lava springs into obsidian, put out fire, and break torches. Egg arrows spawn chickens upon impact with the ground, but there’s a secret too.”

Windows:
1) Open up %appdata%, if you don’t know how to do this, start>run, then type in %appdata%
2) Browse to .minecraft/bin
3) Open up minecraft.jar with WinRAR or 7zip.
4) Drag and drop the necessary files into the jar.
5) Delete the META-INF folder in the jar.
6) Run Minecraft, enjoy!

Macintosh:
1) Go to Applications>Utilities and open terminal.
2) Type in the following, line by line: